So to paraphrase the OP I read him as saying:
Rubbish, I don't agree with you and here is a list of reasons why?
"What you said is rubbish. I don't agree with you and here is a list of reasons why."
Now, can you tell me what value there is in the "What you said is rubbish" part? Let's go one step further: what do you lose by omitting that part?
Mind, I'm just as sick as the next guy of the whole "we must never be negative", politically correct thought police that has been taking politeness to unrecognizable and unreasonable extremes. Sometimes there are good reasons to be aggressive or less than polite, but "sometimes" is not the same as "always" or "most of the time" or "as often as I feel like it".
Sure, there are many ways the OP could have phrased his response.
Personally, I don't think the approach use to attack someone else's point of view is that important, provided the attack is aimed at the message and not the messenger.
In this case I don't think the OP said anything about the messenger.
I don't have a problem with it, but it is the same semantics as what started this whole issue - though he does expand into a list of reasons (which isn't possible on twitter).
Now, granted the word can take on different levels of intensity depending on the circumstances in which it is used.
But it can and is used in general conversation and in that context it means nothing more than "I don't agree with you".
At least that is how the term bullshit is used here in Australia.
For what it's worth, I think most of the commentors are reading far too much into "this is an eye-bleeding script*.
I've seen people hurt by having what they've said called 'bullshit' by someone they respect; it's capable of emotional harm as well. That being said, let's not walk on eggshells.